Arc Flash Fault is a disastrous electrical accident in power system, for example, in the switchgear, which is an explosion of heat, hot gases, and molten metal usually caused by a short circuit of energized conductors. To protect workers and power equipment against this hazard, arc fault protection system is needed. A number of equipment fire and burndown cases arising from low-level arcing faults have been reported in the past. The conventional protection devices relying upon the change in device voltages and currents cannot detect the low-level arcing faults. The reason is that the low-level arcing faults do not cause significant changes in device voltages and currents. The ordinary protection devices themselves are involved in the burndown taking place in the switchgear and let the fault propagate like a chain reaction.
The arc fault protection systems based on arc light detection have been widely used. However, such systems are easily disturbed by ambient light, which may cause a false operation. And these systems can be activated only after the arc flash occurs, so the fault response time enlarges the impact of the arc flash fault on the switchgear system. Another detection technique based on four different types of sensors (ultrasonic, infrared, radio-frequency and acoustic radiations) has been proposed, which compares the incoming signals with pre-set thresholds to decide if the arcing fault has taken place. But this detection scheme has strict requirements regarding the placement of various sensors and the setting of these thresholds, which decreases the efficiency of the detection.
There are solutions which use an expensive optic-fiber microphone as the sensor to pick up the arc sound, and compare the sound pressure level of the arc sound signal or the energy of certain sub-bands of the arc sound signal with a pre-determined threshold to judge if the arc fault occurs. These solutions are not effective because the detection logic is too simple and easily disturbed by environment noise or electrical background noise.